Armor disassociated from the mesh, how to associate again correctly?
The answer you've found is misleading: start with a previous version of your file (the one which worked well in Blender but not in UE4).

Delete the two keyframes that are causing the sliding of the rig in object mode: it's better to have all your animation performed by bones only, not bones movements and object mode movements; expecially for exporting purposes.



Then set the dopesheet window as "action editor", press the "F" button to save the animation even if not used, and click the "X" button to disable the animation.



Select the mesh, delete the armature modifier and apply the multires modifier.

Now you should have both the mesh and the armature in the centre of the scene, in T pose; if not, move them manually to have their locations matching well in the center of the scene.

Select the mesh and use Ctrl A to apply loc, rot and scale of the character, then do the same for the rig.

In edit mode add a new bone, call it "root", set it in the center of the rig, under the feets, in any z and y location you want (it doesn't matter), uncheck its "deforming" property.

Here is the misleading part of the answer: you have to set child of the root bone every other bone which hasn't already a parent, probably you will want to set the two shoulders bones as child of the hip bone, and the hip and the two ankles child of the root bone.

Check in the outliner: the root bone should result parent of every other chain of bones.



Now add an armature modifier to the mesh, setting the armature in its "object" field; in the action editor select your animation: the character will "walk in place"; use the root bone to set two keyframes to have the walking mesh sliding.

Every animation maden with this setup should be imported by UE4 without problems (maybe you will have to unparent again the mesh from the rig, for avoiding crashes) so, if the old animation doesn't work you should redo it with this new rig.